1.Field of the Invention
This invention relates generally to a method of and an apparatus for composing digital tone signals, and more particularly to a digital tone composing system capable of composing a tone signal of digital representation.
2. Prior Art
According to the prior art, there has been proposed a tone composing system in which a waveform is stored in a memory such as a read-only memoty (ROM) in the form of an amplitude value or an increment value of the amplitude at each sampling point and it is read out with a frequency corresponding to the number of sample points N times f (f being the frequency of the tone to be pronounced) whereby the desired digital tone signal is obtained. Such a digital tone signal representation with for example a binary code is modulated by a digital signal which indicates the keying envelope as necessary, then converted to the corresponding analog signal through a D-A converter circuit, amplified and sounded. Such a tone composing system is advantageous in that the desired digital tone can be obtained easily by storing in a ROM various waveforms to be sounded. On the other hand, a large capacity ROM is needed for the storage of the waveform and the hardware volume as a whole increases. Such a disadvantage is unavoidable.